In turbomachines, in particular in compressors and hydraulic pumps but also in turbines, instable flow states and greatly increased losses result during partial and overload operations. On the one hand, the instable flow states result in strong pressure fluctuations which may damage the blade structures. On the other hand, the flow may completely collapse in the compressors and hydraulic pumps in a throttled state. This limits the operating range of the turbomachine and may result in damage to the turbomachine when admissible limits are exceeded.
The instable flow state is primarily caused by the flow separation on the individual blades in the cascade system. To suppress the separation, a temporarily changed inflow may lead toward the blades. In one known measure, the blade affected by the separation oscillates around an axis of suspension. In another measure, oscillating blades are located in the inflow of the blades affected by the separation, whereby a harmonic, oscillating inflow is generated toward the blades. One example is an oscillating system of initial stationary blades. Another measure provides that a fluid is introduced through blow-in locations distributed over the periphery, which has a flow angle and/or a flow momentum deviating from the main flow, and thereby the inflow of the blades affected by the separation is locally changed. The disadvantage of these active measures is, however, that, on the one hand, energy, which must be taken from the overall process, is needed to influence the flow, whereby the overall efficiency is reduced. On the other hand, to implement these measures, complex constructive and regulative changes are necessary which result in an increased development effort, an increased susceptibility to errors, and an increased weight of the machine.
Furthermore, passive measures are known in which the blades of a blade cascade are profiled differently and/or are arranged asymmetrically in the blade cascade. DE 10 2008 049 358 A1 thus proposes to profile the blades of a compressor inlet guide baffle in such a way that a symmetric outflow from the blade cascade takes place in the case of an asymmetric inflow. For this purpose, the blades each have a changed front blade area. In GB 2 046 849 B1, a stationary blade arrangement having an asymmetric arrangement of stationary blades is shown whose rear edges are located on a line viewed in the peripheral direction and thus in identical axial position. EP 1 508 669 A1 shows a measure in which the blades of an initial guide baffle are profiled differently to take into account an asymmetric incident flow of a ring of initial stationary blades.